Opaque composition for forming a windowed web in a cathode ray tube screen structure

ABSTRACT

AN IMPROVED OPAQUE COMPOSITION WHICH IS FORMULATED TO BE UTILIZED IN A MINIMAL STEP PROCESS FOR FORMING A UNIFORM OPAQUE INTERSTITIAL PATTERN FOR A COLOR CATHODE RAY TUBE SCREEN STRUCTURE. THE OPAQUE COMPOSITION, CONTAINING A HIGH PERCENTAGE OF AN ORGANIC SOLVENT, IS DISPOSED IN A MANNER TO FORM AN OPAQUE INTERSTITIAL WEB HAVING MULTITUDINOUS WINDOWS THEREIN WHEREIN PHOSPHOR PATTERN ELEMENTS ARE SUBSEQUENTLY DISPOSED.

United States Patent 1' heel 3,667,986 Patented June 6, 1972 3,667,986 OPAQUE COMPOSITION FOR FORMING A WINDOWED WEB IN A CATHODE RAY TUBE SCREEN STRUCTURE Robert A. Hedler, Seneca Falls, N.Y., assignor to Sylvania Electric Products Inc. No Drawing. Filed May 28, 1970, Ser. No. 41,530 Int. Cl. B44d J/02, /00; C03c 17/00 U.S. Cl. 117-335 CM 5 Claims ABSTRACT OF THE DISCLOSURE 7 CROSS-REFERENCES T 0 RELATED APPLICATIONS This application contains matter disclosed but not claimed in two related United States patent applications filed concurrently herewith and assigned to the assignee of the present invention. These related applications are Ser. No. 41,536, and Ser. No. 41,535, both filed May 28, 1970.

BACKGROUND OF THE INVENTION This invention relates to the manufacturing of cathode ray tubes and more particularly to an opaque coating composition utilized in forming a portion of a color screen structure.

Cathode ray tubes capable of presenting multi-color display imagery, such as those employed in color television applications, conventionally utilize patterned screens comprised of repetitive groups of related phosphor materials. These groupings are nomally disposed as bars, stripes or dots depending upon the type of color tube structure considered. For example, in the well-known shadow mask tube construction, the screen pattern is conventionally composed of a vast multitude of dots formed of selected cathodoluminescent phosphors, which, upon predetermined excitation, produce additive primary hues to provide the desired color imagery. The individual dots comprising the screen pattern are often in substantially tangential contact With one another, while in other instances they are separated by relatively small interstitial spacings provided to enhance color purity by reducing the possibility of electron excitation of adjacent dots. Associated with the screen and spaced therefrom is a foraminous structure or shadowrnask. Each of the apertures therein is related to a specific grouping of dots of the screen pattern in a spaced manner to enable the selected electron beams traversing the apertures to impinge theproper dots therebeneath.

To improve brightness and contrast of the color screen image a screen structure has been developed wherein a dot-defining interstitial spacing is effected between the dots in the form of an opaque light-absorbing material. In essence, each phosphor dot is encircled or defined by a substantially dark encompassment which collectively comprise a foraminous pattern in the form of a Windowed webbing having an array of substantially opaque connected interstices. Such web-like structures have been fabricated, either before or after screening, by several processes wherein photo-deposition techniques play a prominent role. Some of the methods achieve a web-like opaque interstitial pattern by including convertible pigments in a photosen'sitized liquid applied to the viewing or face panel of the tube. By a subsequent heating step, these pigment materials are converted or darkened to produce the desired opaque quality. From a production consideration, the multiplicity of required steps are normally time consuming in view of various degrees of complexity. Additionally, in certain instances the cost of the materials and the necessary steps involved make the processes expensive in consideration of the results obtained. In other processes where water dispersions of carbon formulations are employed, the coating has a tendency to be less uni-..

form and is prone to shale or scale, both conditions being deleterious factors to achieving the desired web-pattern. Furthermore, another deterrent is sometimes evidenced in those procedures wherein the opaque webbing is disposed subsequent to screen pattern formation, wherein there is the possibility of extraneous opaque material contaminating the respective phosphor dots of the screen.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned disadvantages and to provide an opaque composition for expeditiously forming a compact and uniform opaque interstitial webbing that is free from shale for a color cathode ray tube screen structure. Another object is to provide an opaque composition for use in an interstitial web-forming process wherein a minimal number of processing steps are required, and one that is readily adaptable to production techniques.

The foregoing objects are achieved in one aspect of the invention by providing an opaque composition for use in a process wherein the interior surface of the panel is first coated with a thin uniform layer of a polyvinyl alcohol solution photosensitized with a dichromate material. The coated panel is then exposed by beaming light through the multiple openings of the pattern mask to polymerize the pattern therein. Next, the exposed panel is developed to remove the unpolymerized areas thereby providing a polymerized screen format pattern surrounded by a web pattern of substantially bare glass. Following this, the panel is overcoated with an opaque composition in the form of a colloidal suspension of graphite that utilizes a high percentage of an organic solvent and produces a uniform coating that is free from shale. The opaque coating is then treated with a suitable developing agent to effect an effervescence to degrade the screen format pattern. This degradation reaction also loosens the contiguously associated graphite thereover. The loosened materials are then removed by pressurized water development to produce an opaque interstitial web having multitudinous windows therein defining bare glass areas wherein the plural phosphor screen pattern is subsequently formed.

The terms degrade and degradation as used in this specification are intended to denote both physical and chemical decomposition of the polymerized material.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims.

In preparation of the web-forming process, the viewing or face panel portion of the cathode ray tube is cleaned in a normal manner by washing particularly the interior of the panel with a 5-10 percent aqueous solution of hydrofluoric acid, whereupon it is water rinsed. The panel is then precoated, for example, with a 0.3 percent aqueous solution of polyvinyl alcohol and dried in a conventional manner thereby providing a surface consistency to promote uniformity of wetting when the process for forming the web is initiated.

In one embodiment of the process for forming the windowed web on the color tube viewing panel, the interior surface of the panel is coated with a thin uniform layer of a substantially clear polyvinyl alcohol (PVA) solution photosensitized with a chromate material, such as potassium or ammonium bi or dichromate. The dissolved PVA solids are carried in a water-primary alcohol diluent, such as ethyl and/or methyl alcohol; and the amount of photosensitizing material contained therein is preferably greater than the amount normally utilized in screen formation. The sensitized coating material is formulated to provide a thin covering function and exhibits an area density less than that of the conventional application of such material for promoting phosphor adherence. The PVA solution comprises PVA solids ranging from substantially 1.2 to 2.4 weight percent, the water ranges from substantially 43.0 to 64.0 weight percent,

and the primary alcohol ranges from substantially 33.0 to 54.0 weight percent. The chromate solids therein are within the range of substantially 0.2 to 0.3 weight percent. The coating solution as applied, has a viscosity ranging from substantially 3.0 to 5.0 centipoises.

After deposition of the uniform coating, a multipleopening pattern mask, such as foraminous shadow-mask, is positioned within the panel. The coated panel'is then exposed by beaming light through the multiple openings of the mask to light-polymerize discrete portions of the photosensitive panel coating in the areas subsequently occupied by the screen pattern phosphor elements.

The mask is removed from the panel and the exposed coating is developed by rinsing with water to remove the unexposed PVA, thereby providing a web pattern of substantially bare glass defining the interstitial spacings be tween the substantially clear polymerized pattern elements.

The patterned panel is then overcoated with a uniform layer of a substantially opaque colloidal suspension of graphite beneficially utilizing a high percentage of an organic solvent. An exemplary embodiment is a suspension comprised of substantially 15 weight percent of a 22 percent homogeneous graphite dispersion in Water, such as Aquadag formulated by Acheson Colloids Company, Port Huron, Mich.; to which is added substantially 40 weight percent of water; and substantially 45 weight percent of a suitable water miscible organic solvent. This water miscible organic solvent is at least one alcohol selected from the group consisting of ethyl alcohol, methyl alcohol, isopropyl alcohol, and normal propyl alcohol. Functionally, it has been found that a high percentage of inclusion of one or more of the above-noted alcohols determines certain beneficial characteristics of the opaque composition which are not fully realized in straight water dispersions. For example, the high percentage of alcohol influences the wetting ability, the leveling or uniform coverage of the composition, the drying time, and the defoaming properties. In addition, it has been discovered that a high percentage of alcohol produces a more compact and a more opaque appearing film with a lower concentration of graphite.

Another embodiment has been formulated wherein an effectual opaque composition is comprised of substantially 3 to 6 weight percent of particled natural graphite solids not exceeding substantially three microns in size. These solids are dispersed in a liquid vehicle wherein water comprises 40 to 70 weight percent of the total com position and one or more of the above-mentioned water miscible organic solvents, 20 to 50 weight percent. The application viscosity of the opaque suspension ranges substantially from 5 to 6 centipoises.

In formulating the coating composition, the graphite material is substantially a 22 weight percent pre-dispersion in water to which additional water is added in the range from substantially 27 to 41 weight percent, with '4 t the remainder of the composition not exceeding substantially 50 weight percent of the afore-mentioned water miscible organic solvent. Preferably the water and alcohol additions to the pre-dispersion are in the order of substantially 40 weight percent of Water and substantially 45 weight percent of the organic solvent material.

In greater detail, the pre-dispersion of the opaque pigment is in the form of substantially 22 weight percent of particled material graphite solids in substantially 35 to 36 weight percent of water. The micro-particled graphite solids are available from the Joseph Dixon CrucibleCompany, Jersey City, NJ. and from Asbury Graphite Mills, Inc., Asbury, NJ. Included in the pre-dispersion are not more than 10 weight percent total of a compatible film former, a dispersant and a plasticizer. For example, the film former, which is present in from substantially 6 to 7 weight percent is, for example, an acrylic emulsion polymer such as Rhoplex B-74 available from Rohm and Haas Company, Philadelphia, Pa. The dispersant, which is included in the amount of 1.0 to 1.5 weight" percent, is, for example, a polyacrylic acid in the form of a stable hydrophilic colloid such as Aerysol A-3, supplied by Rohm and Haas Company, Philadelphia, Pa. The noted plasticizer, which is present in from 1.0 to 1.5 weight percent is, for example, a dihydroxyl alcohol or glycol such as 1,2-ethanediol. Also included in the pre-dispersion is an appreciable amount of a compatible wetting agent in the form of 28 percent ammonium hydroxide. This reagent comprises substantially 33 to 35 weight percent of the pre-dispersion.

An application coating dispersion is formed by including at least 20 weightv percent of the aforedescribed predispersion to which is added at least 25 weight percent of water and not more than 50 weight percent of at least one water miscible organic solvent selected from the aforementioned group of alcohols.

Upon applying the coating, opaque film formation is accomplished by heating the panel in the temperature range of substantially 100-l20 degrees Fahrenheit until the coating is dry.

After drying the overcoated panel is then treated at substantially room temperature, i.e., about 7278 degrees Fahrenheit, with a compatible water-soluble degrading agent to effect an effervescence and degradation of the screen pattern element areas of light-polymerized material and loosen the associated graphite contiguous thereon. The degraded materials and loosened graphite are then removed by pressurized water thereby providing an opaque interstitial web having multitudinous windows therein defining bare glass areas wherein cathodoluminescent phosphors are subsequently disposed by conventional techniques to form the screenpattern elements.

Thus, an advantageous and improved opaque composition is provided for use in the process for forming a windowed web foundation pattern for a cathode ray tube screen structure wherein the phosphor elements of the screen pattern are subsequently disposed. The high percentage of alcohol in the formulation provides a more uniform and compact film and one that is more opaque with a lower concentration of graphite. Since the opaque interstitial webbing composition, discretely defining the utilized areas of the respective phosphor elements, is ap plied prior to screening and requires no pigmentary conversion, there is little opportunity for phosphor contamination. The process utilizing the opaque composition involves a minimal number of steps and is readily adaptable to productiontechniques.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein without departing from the scope of the inventionas defined by the appended claims.

I claim:

*1. In a multi-color cathode ray tube having formed on the surface of the face panel thereof a patterned cathodoluminescent screen comprising multitudinous repetitive phosphor elements separated by an interstitial web of opaque material of substantially uniform thickness, an opaque coating composition utilized in the forming of said web as a multi-windowed pattern on the interior surface of said panel prior to the deposition of said phosphor elements thereon, said coating composition comprising:

particled natural graphite solids not exceeding substantially three microns in size, said graphite solids being present in the range of from substantially 3 to 6 weight percent;

water in the range of from substantially 40 to 70 weight percent, and

a water miscible organic solvent in the range of from 20 to 50 weight percent, said graphite being dispersed in said water and said solvent to provide a coating viscosity ranging substantially from 5 to 6 centipoises.

2. The multi-color cathode ray tube according to claim 1 wherein said water miscible organic solvent of said opaque coating composition is at least one selected from the group consisting of: ethyl alcohol, methyl alcohol, isopropyl alcohol and normal propyl alcohol.

3. The multi-color cathode ray tube according to claim 1 wherein the opaque coating composition is a suspension comprised of at least 9 Weight percent of a 22 percent homogeneous graphite pre-dispersion in substantially water, to which additional water is added in the range of from substantially 27 to 41 weight percent, and wherein the water miscible organic solvent content of said composition does not exceed substantially 50 weight percent.

4. The multi-color cathode ray tube according to claim 1 wherein the opaque coating composition is a suspension comprised of substantially 15 weight percent of a 22 percent homogeneous graphite pre-dispersion in substantially water, to which there is added substantially 40 weight percent of additional Water and substantially 45 weight percent of said water miscible organic solvent.

5. In a multi-color cathode ray tube having formed on the surface of the face panel thereof a patterned cathodoluminescent screen comprising multitudinous repetitive phosphor elements separated by an interstitial web of opaque material, an opaque coating composition employed in the forming of said web as a multi-windowed pattern on the interior surface of said panel prior to the deposition of said phosphor elements thereon, the formulation of said coating composition comprising:

(1) forming a pre-dispersion of an opaque pigment in the form of substantially 22 weight percent graphite solids in water, and including a wetting agent in the form of ammonium hydroxide in an amount not exceeding 35 weight percent of said pre-dispersion; and

(2) forming said web coating composition to include at least 20 weight percent of said pre-dispersion to which is added at least 25 weight percent of additional water and not more than weight percent of at least one water miscible organic solvent selected from the group consisting of ethyl alcohol, methyl alcohol, isopropyl alcohol, and normal propyl alcohol to provide a coating viscosity ranging substantially from 5 to 6 centipoises.

References Cited UNITED STATES PATENTS 3,330,682 7/1967 Tamura 1l733.5 CM 2,496,901 2/1950 VanHoorn 1l7-33.5 CX 2,176,879 10/1939 'Bartell 252-309 X 3,317,337 5/1967 Saulnier 117-33.5 CP 1,981,652 11/1934 Long 117226 X ALFRED L. LEAVIIT, Primary Examiner K. P. GLYNN, Assistant Examiner US. Cl. X.R.

117124 A, 226, 169 R; 2'52--309, 313 R 

